This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-236170 filed on Aug. 3, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a disc-type commutator for an electric rotating machine.
2. Description of Related Art
A disc-type commutator mounted on an axial end of an armature of an electric rotating machine such as a fuel pump motor or a starter motor has been known hitherto. There are two types of disc-type commutator. One is a separate type which is made separately from armature conductors and mounted on an armature end surface. The other is a unitary type which is made integrally with armature conductors. In those disc-type commutators, commutator segments are arranged in a radial direction on an axial end surface of an armature, and segment gaps between commutator segments are open to the axial end surface that constitutes a commutating surface. A width of the segment gap is made as narrow as possible to effectively utilize the commutating surface and to reduce a current density on the commutating surface.
By using the disc-type commutator, it is possible to shorten an axial length of an armature, compared with an armature using an cylinder-type commutator. However, there has been a problem in the conventional disc-type commutator. That is, swarfs generated in a process of machining the commutating surface enter into the segment gaps that are open to the commutating surface, and it is difficult to remove those swarfs from the segment gaps. Further, brush dusts and other foreign particles entered into the segment gaps during operation of the rotating machine are not easy to remove from the segment gaps. When the cylinder-type commutator is used, such dusts or foreign particles can be removed by a centrifugal force generated by rotation of the armature. It is difficult, however, to remove the foreign particles from the segment gaps of the disc-type commutator. If such foreign particles remain in the segment gaps, a proper insulation between segments cannot be maintained, or abnormal abrasion of brushes may occur. This may result in malfunction of the commutator.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved disc-type commutator in which foreign particles entered into the segment gaps are easily removed.
The disc-type commutator is composed of an insulating disc and plural commutator segments radially disposed on the insulating disc, forming a commutating surface. The commutator segments are separated from one another by segment gaps formed between neighboring commutator segments. The disc-type commutator is mounted on a rear end surface of an armature of an electric rotating machine so that the commutator surface is positioned perpendicularly to a rotating axis of the armature. Conductors forming an armature coil disposed in slots of an armature core are electrically connected to the commutator segments. One end of the segment gaps in the axial direction is open to the commutating surface and the other end is closed by the insulating disc.
A width of the segment gap in a rotational direction of the armature is narrow at the radial inside of the commutator and gradually widened toward the radial outside. The width may be made more than twice wider at the radial outside than at the radial inside. Swarfs entered into the segment gaps in a process of machining the commutating surface and foreign particles such as brush dusts entered during operation of the rotating machine are easily removed from the segment gaps by a centrifugal force generated by rotation because the segment gaps are widened at the radial outside.
Further, the width of the segment gap is gradually widened along the axial direction, so that the segment gap is the narrowest at its closed end contacting the insulating disc and the widest at its end open to the commutating surface. The segment gap may be widened symmetrically with respect to the axial direction, or asymmetrically widened by making a forward side surface of the commutator segement facing the rotational direction slanted more than a backward side surface.
According to the present invention foreign particles such as swarfs or brush dusts entered into the segment gaps can be easily removed, and thereby commutator functions are properly maintained for a long time.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.